Coastal
CffiIf m I]llt
~~ffi
Cornell
CONTROL
IN
.
University
OF
RESIDENTIAL
ZEBRA
WATER
State
Resources
FACT
July
University
1993-
Revised
SHEET
8196
of New York
MUSSELS
SYSTEMS
Charles R. O'Neill, Jr.
New York Sea Grant Extension Specialist
Introduction
byssal threads) tipped with a natural adhesive akin to
that produced by barnacles. Once attached, zebra musThe zebra mussel, Dreissenapolymorpha and Dreissena
sels reproduce in prolific numbers and colonize extenbugensis, is a small bivalve mollusk (a clam-like shellfish
sive portions of large-scale water handling facilities,
with two matching shell halves; Fig. 1) that has invaded
greatly reducing pumping efficiency -even totally clogNorth America's fresh surface waterbodies from Duluth
ging smaller pipes.
to Massena, New York; from Chicago to Vicksburg,
Zebra mussels are also capable of clogging the small
Mississippi; and from Nashville to Little Rock. Since their
water intake pipes found in private homes and cottages
initial discovery in Lake St. Clair in 1988, the mussels
along North America's many inland lakes, streams, and
have spread rapidly throughout allot the Great Lakes,
rivers (they have already begun to clog some residential
the Hudson River, the St.
systems in parts of the G reat
Lawrence River, much of the
Lakes and Finger Lakes reMississippi River Basin, ingions). Conservative esticluding major tributaries
mates place the number of
such as the Tennessee,
private dwellings with threatOhio, and Arkansas Rivers,
ened water systems in the
and parts of the Canadian
eastern
half of North
Provinces of Ontario and
America
at more than
Quebec (Fig. 2. See insert).
100,000.
Biologists believe that transThis publication
is diport of the mussels from inrected at the owners of resifested waters to other ,
dences with private water
unintested inland fresh sursystems. It discusses the
face waters will continue to
several components of such
take place as a result of natusystems and presents a
ral and human activities. In
number of alternative conall likelihood, the mussels
trol and mitigation measures
will ultimately infest most
that can be undertaken to
areas south of central Can- Figure 1. The zebra mussel is a small clam-like shellfish cope with zebra mussels.
ada and north of the Florida capable of attaching to most submerged hard surfaces. Once Not all alternatives will work
Panhandle from the Pacific attached, they reproduce in prolific numbers forming extensive
equally well for all systems;
coast to th'e Atlantic coast
colonies, often totally clogging water intake pipes
most will need to be fineh
.
f
20 t ' Copyright
1991ScottCamazine
per aps In as ew as
o
tuned to match up with the
25 years.
particular system being retrofit. It is recommended that homeowners engage the
The most highly visible impact of the zebra mussel
services of a qualified plumbing contractor to develop
has been its fouling of large-scale raw water intakes,
and install the best alternative for a given situation.
such as those at industrial and electric generation faciliLocal, state, or provincial permit authorities should be
ties and municipal drinking water treatment plants. These
consulted to determine what, if any, permits might be
facilities are vulnerable because the mussels are carequired for construction or installation of control projects.
pable of attaching to most submerged hard surfaces
(substrates) by means of tough elastic fibers (called
The Threat to Small
Water Systems
Why are zebra mussels
a
threat to large-scale and residential water systems? Water intake structures
(pipes
and theirsupporting
cribwork)
serve as an excellent habitat
for zebra mussel colonization. The continuous
flow of
water into the pipes carries
with it a continuous source of
food and oxygen for the mussels and carries away their
wastes, while the structures
themselves
protect the mussels from predation and environmental conditions such as
storm
wave
activity
and
scouring by ice.
The zebra mussel can attach to intake pipes at water
Figure 3. Residential water systems have two parts: an offshore component from the lake/river
end of the pipe to the pump on the shore; and, an onshore component from (and including) the
pump to the distribution pipes and faucets inside the residence.
flow velocities
of approximately 6.5 feet (2 meters) per second and below. In
some large public facilities, layers of mussels up to 2 feet
(.61 meters) thick have been observed. The typical 1- to
2-inch (2.54- to 5.1-centimeter)
diameter
residential
pipe simply doesn't stand a chance against an organism
capable
of such fouling.
Zebra mussels enterwater
intakes via several mechanisms: in the form of veligers (microscopic
larvae) they
are carried by the water flow; as juveniles, they can crawl
in using their clamlike foot; and as adults they can break
loose from colonies and travel to the mouths of intakes
by lake or river currents.
Mussel spawning can take place during the time of
the year that surface waters are approximately
50°F
(10°C). Zebra mussel veligers hatch from eggs at a size
of approximately
70 microns (.00275 inch). Both shallow
and deep intakes are affected
since zebra mussels
generally colonize from 2 feet (.61 meter) of the water
surface down to depths of 200 feet (61 meters) or more.
Why hasn't more been heard about the clogging of
residential
water systems?
Actually, there have been
private residential systems fouled on the Great Lakes,
as well as in the Finger Lakes in New York State. The
number of systems fouled to date may be small because
of several reasons.
First, there may be many such
systems in which failure is imminent but in which water
flow has not yet gotten bad enough to be reported to local
health departments
or other authorities ( or even noticed
by the owners). Second, such small systems are drawing in relatively small amounts of water per day (250 to
400 gallons per day (gpd]; 946.4 to 1514.2 liters per day
(Ipd], for a 3-bedroom
year-round
residence,
perhaps
only an intermittent
25 to 100 gpd (94.6 to 378.5 Ipd] for
a weekend cottage) compared
to larger municipal,
in2
dustrial,
and power
facility
systems
(hundreds
of thou-
sands or even millions of gpd). Residential systems are,
therefore,
taking in far fewer zebra mussel veligers
compared to larger systems and are suffering the consequences
slower and later than the larger systems.
Finally, zebra mussel colonization
tends to be spotty
along the shoreline of any given waterway,
particularly
in the early stages of infestation.
Given such spottiness
and the high degree of variability
of mussel veliger
densities
in the water column, larger systems have a
much higher
than smaller,
probability
residential
of early (and heavier)
systems.
impact
Once in a water intake line, zebra mussels
can
colonize any part of the system from the mouth of the
intake in the lake or river to the distribution
pipes within
the residence.
Impacts of this colonization
include loss
of pumping efficiency, obstruction
of foot valves, putrefactive decay of mussel flesh, production of obnoxioustasting and foul-smelling
methane gas, and increased
corrosion
of steel, iron, and copper
pipes.
The first indication that zebra mussels are in a water
intake is usually the discharge of shells or shell parts at
the shore end of the pipe, a noticeable
decrease
in
pumping head (water volume and pressure), or obnoxious tastes and odors in the water. The rate of overgrowth and clogging of water intakes by zebra mussels
depends upon a number of factors, including the chemical and physical characteristics
of the waterbody,
the
velocity
and volume
of flow within the system,
the
positioning of the intake end of the pipe in the waterbody ,
the material the pipe is made of, and the type and
amount of natural substrate (such as rock) around the
intake. Mussel densities in industrial intake canals and
pipes have been recorded
as high as 627 ,000 per
square
yard (roughly
750,000
per square
meter).
rather than offshore component, this area will be addressed first.
Control
in the
Onshore
Figure 4. A 25-50 micron (absolute) in-Iine filter capable of filtering the total water consumption
needs of a household (250-400 gpd for a year-round home of a family of four) installed in the
onshore component to keep zebra mussel veligers and shells out of a house's interior plumbing.
Control
Alternatives
Experience with public and industrial water intakes has
demonstrated that it is best to eliminate zebra mussels in
water intake pipes at the veliger stage or before juvenile
mussels are able to pass unhindered into critical areas of
the water system. In other words, the mussels should be
killed or removed from the system before they get into
areas that are difficult to clean, and before the mussels can
attach, grow, and become problematical. Control can be
continuous (no mussels tolerated, ever), or periodic
(some mussel growth allowed until no longer tolerable,
followed by removal, the removal schedule being based
upon the rate of colonization in that particular system).
Given the foul tastes and odors associated with zebra
mussels in water intakes, most homeowners will probably
choose to tolerate few or no mussels in their systems.
When considering the potential clogging of a private
residence water intake system, homeowners should view
the system in two parts. Part 1 is the onshore component, that part of the system from (and including) the pump
to the distribution pipes and faucets inside the residence,
including the piping between the pump, the house, and
any storage tank. Part 2 is the offshore component, that
is, the pipe from its intake end in the lake or river to the
pump on the shore (Fig. 3).
The onshore component will, in most cases, be the
simplest and least expensive section to protect but the
most difficult and costly to clean out if infested (because of
the difficulty of physically removing plugged pipes from
within the walls of a house). On the other hand, in most
situations, the offshore component will be the most difficult
and expensive section to protect against clogging by zebra
mussels but the least difficult section to remediate (clean
out) once it does become infested (pg 9). As control of the
mussels is more easily accomplished in the onshore
of Zebra
Mussels
Component
Homeowners
using a zebramussel-infested
waterbody as
a water source are advised to
take early action to keep the
mussels out of the onshore
component
of their systems
before the systems become
infested.
Alternatives for accomplishing
this goal include
installation of a replaceable or
cleanable in-Iine filter, chlorination, or a combination
of
filtration and chlorination.
Wh i Ie sc reen i n g o r
straining the water in the offshore component,
at the in-
take (lake or river) end of the
pipe, is an obvious method of protecting a residential water
system from zebra mussel infestation, this alternative is a
very difficult undertaking of questionable effect, and will be
discussed below.
In-Iine Filtration
In-Iine filtration is a far more easily accomplished control
alternative for the onshore component. This involves the
installation of a "whole house" in-Iine filter on the water line
(either ahead of or behind the pump, depending upon the
specific type of pump in use) priorto the pipe's entrance to
the in-the-house distribution (plumbing) system (Fig. 4).
All water used by the residence passes through the filter
before distribution. Such a filter must be capable of filtering
the maximum total amount of water reasonably expected
to be used bya private residence in a day (250 to 400 gpd
[946.4 to 1514.2 Ipd] for a full-time residence of a family of
four, perhaps as little as 25 gpd [94.6 Ipd] for a seasonal
weekend cottage) , and be capable of removing all particulate matter larger than approximately 50 microns (about
.00196 inch), effectively keeping out particles 20 microns
(.00079) smaller than the size of a zebra mussel veliger.
Flow rates of 6-20 gpm (22.7 -75.7 Ipm) will be needed to
serve the needs of a year-round residence.
In-Iine whole house filters come in a variety of configurations, including:
.single-media
filters containing fiber or filamentous "angel
hair"-like media, able to remove particles down to 25 to
50 microns (.00098 to .00196 inch);
.dual-media
filters with fiber media surrounding a center
section of activated charcoal capable of filtering down
to 20 microns (.00079 inch) or smaller and removing
many flavors and odors; and,
.backflushable
filters or strainers that clean, rather than replace, the filter media by reversing the water flow and flushing
the trapped particles from the filter, much like a swimming pool filter.
All in-Iine filters require either periodic media replacement or backflushing. The amount of time between cleanings will
depend upon: (1) the amount of silt, algae, zebra mussel veligers, and other materials drawn into the system; (2) the
location the waterbody; and (3) the time of year. Caution should be used when cleaning or replacing filter media to ensure
that none of the trapped material is inadvertently allowed to bypass the filter, thus contaminating the system.
At this writing, a good single-media filter can be obtained from plumbing supply houses for less than $200; dual-media
filters can cost up to approximately $300; and backflushable filters can cost from $200 to $400 or more. Installation bya
plumber adds to the initial cost
of in-Iine filtration systems. The
replacement of clogged filter
refills is an ongoing cost and
time commitment
for the
homeowner.
Chlorine Injection
Another method of preventing
colonization in the onshore
portion of a residential water
system is the installation of an
in-Iinechlorine injector afterthe
pump, before the water enters
the in-house distribution system (Fig. 5). Such systems add
a small amount of potable chlorine to the incoming water every time the pump runs. The
amount of chlorine injected is
comparable to that added to
municipal water for disinfection
purposes priorto being pumped
to consumers, about 0.25 ppm
TRC (parts per million total residual chlorine). This amount,
added each time water is drawn
from the lake or river, is sufficient to kill zebra mussel veligers, juveniles, and adults
being drawn into the system
with the water, and will keep the
in-house plumbing clean of zebra mussels. (This may have
the added benefit of improving
the water potability by destroying other pathogens, such as
bacteria- homeowners should
check with their county health
department or Cooperative
Extension Service for guidelines on human consumption of
lake or river water.) A chlorinatorwill not, however, keep shells
and shell fragments drawn in
from the lake or river from clogging faucets; a filter should be
used in conjunction with a chlorinator for best effect (Figure
5a).
4
Figure 5. An in-Iine chlorine injection system, dosing at 0.25 ppm TRC every time the pump
operates is designed to prevent the settling and growth of zebra mussels; it does not keep out
shells.
Figure Sa. The combination of a 25-50 micron (absolute) in-Iine filter capable of filtering (250400 gpd for a year-round home of a family of four) installed in combination with an in-Iine
chlorine injection system, dosing at 0.25 ppm TRC whenever the pump runs, should ensure
that the onshore component will remain mussel-free and will improve the quality of the water
in the process.
~
Shore Wells and Cisterns
In some locales, specifically those
with a sand and gravel shoreline, an
old shoreline residence water source
may be ready for a comeback -the
use of shore wells and shoreline
cisterns. Shore wells and cisterns
utilize sand and gravel to filter out
particulate materials, including zebra mussel veligers. In its simplest
form, a shore well consists of a pipe
tipped with a "well point" driven into a
sandy shore until the point penetrates
into the low water water table associated with the river or lake. The pipe
must penetrate the low water table to
ensure a constant flow of water even
during drought conditions. This alternative requires a very sandy shoreline with little or no rock to allow the
well point to be driven down to the
water table, and is usually only applicable for low-flow systems, such as
seasonal or weekend cottages.
Another approach is to drill or
dig a cistern approximately 24 to
36 inches (60.96 to 91.44 centimeters) in diameter deep enough to
penetrate at least several feet into
the low water water table. The
sides of the cistern should be
sleeved with either a plastic, concrete, or metal liner to prevent its
caving in and to serve as a holding
area for water infiltrating from the
watertable. Waterwill infiltrate into
the cistern from the open bottom of
the casing; the liner can also be
perforated at the bottom where it
penetrates the water table to facilitate water infiltration (Fig. 6). The
cistern should be located far
enough landward from the water's
edge to place the top of the well
above the high water wave run-up
line to prevent overtopping during
storms. The cistern should have a
watertight cover installed to pre-
Lockable, overlapping,
tight cover
---
.- --
-
-~~
/
4" Top
/
./
/
"'-.-
112'
/
/
SO~
""'
Clay
!
/
Sand
\ Ground
level
Concrete, metal,
or plastic casing
2'
"'"
,,
-..
,~
Water
table
\
-Pump
\
\
Limit of excavation ~
-Support,
"
" Clean
gravel
or foot valve
if needed
or pea stone
Figure 6. In the shoreline cistern, a 24- to 36-inch diameter cistern is dug down into the
low water water table. A plastic, concrete, or metal liner prevents caving in and serves
as a holding area for water infiltrating from the water table.
Figure 7. Where hardpan or bedrock near the surface precludes water infiltration into
a shoreline cistern, a sand-and-gravel-filled channel can be installed between the
cistern and the water source.
vent contamination. The pump can
either be installed in the cistern or outside the cistern in
a wellhouse with a pipe running into the cistern.
Neither shore wells nor cisterns are practical in areas
with rocky shorelines or with shallow bedrock. In some
cases, this problem can be overcome by digging a pit
much larger than the diameter of the cistern itself (6 to 10
feet [1.83 to 3.05 meters], for example), positioning the
cistern casing in the center of the pit, and filling the pit with
coarse sand and gravel around the casing (Fig. 7). A
channel is dug, connecting the cistern to the lake or river.
The channel, like the cistern pit, is filled with coarse sand and
gravel. Water from the lake or river percolate through the
channel into the pit. Water percolates into the cistern, where
it is then pumped to the residence. The cistern physically
excludes mussel veligers and other particles as the water
passes through the sand and gravel. The entire structure,
channel and pit, is capped with a layer of impermeable clay to
prevent contamination of the cistern by overland flow.
While a shoreline cistern can remove zebra mussel
veligers and other particles, it may not provide potable
5
water without the addition of some form of disinfection.
Readers should consult with their county Cooperative
Extension Service or health department for information on
potable water supplies.
One major drawback associated with all forms of shore
wells and cisterns is that in many areas, septic system
leach fields have been placed close to the top of shoreline
banks or bluffs and may result in the infiltration of septic
leach ate into the shallow shoreline aquifer (water supply),
thereby contaminating the wells. Shore well or cistern
water should be tested before it is used for drinking
purposes. Cooperative Extension water education specialists or health department staff can provide information
on such contamination.
Wells
Perhaps the most dependable
longterm onshore control
alternative is the drilling of a traditional well. This alternative will, in most cases, be a rather substantial one-time
investment.
In those areas where homeowners
have
chosen not to drill a well because of bad water conditions
(no viable aquifer available, sulfur or salt in the water,
pollution of groundwater,
etc.) this choice may not be a
viable alternative.
Control
in the
of Zebra
Offshore
Mussels
Component
Zebra mussel veligers are so tiny that they pass easily
through screens and strainers and need to be removed in
some other manner before they can settle and colonize
within the distribution system. As mentioned earlier, the
first method most people think of for attempting the control
of zebra mussels in the offshore component of residential
water intakes is preventing the entry of larval, juvenile, and
adult mussels into the pipes by the use of strainers or
screens. The effectiveness
of this control method depends upon the mesh size of screens and strainers and
the size of the mussels being drawn into the intake. The
screen mesh commonly used over small intake pipes (if
any is used at all) is 0.25 to 0.50 inch (.64 to 1.27
centimeters), is intended to keep out pieces of leaves and
other large objects, and would exclude only adult mussels.
Since zebra mussel veligers and young juveniles range
from about 70 microns (.00275 inch) and up, simply using
strainers or screens at the intake is ineffective as a control
strategy and should not be relied upon by owners of
residential systems.
Although the effectiveness of screens or strainers could
be increased by reducing the mesh size, it is impractical to
place a strainer with very small mesh over the end of a pipe
in a waterbody since it will quickly clog with silt, algae, and
debris. Since zebra mussels attach to virtually any hard
surface, offshore strainers or screens are also subject to
directfouling by the mussels they are intended to keep out.
While this can be temporarily minimized by using copper
for screens or strainers (copper ionizes in water; copper
ions apparently prevent zebra mussel attachment),
once
the copper has formed a greenish oxide surface layer,
6
sealing off most of the copper ions, it, too, becomes a
potential mussel attachment surface.
A number of offshore filters are now coming onto the
market. The potential for clogging by silt, algae, debris,
and mussels must be considered by homeowners considering such systems. Enclosing filters in metal, plastic, or
other types of containments in an effort to protect them
from the elements may actually provide a very suitable,
protected habitat for mussel growth around the filters. The
filters themselves, being hard, will also serve as attachment substrate for the mussels, leading to fouling and
clogging. The use of a copper screen around a filter does
not guarantee that zebra mussels will not attach to the
filter, since veligers can pass through openings in the
screen and, later, as the screen oxidizes, attach to the
screen itself.
Homeowners considering such new systems should
request that sellers provide detailed information on how,
how long, when, and where the systems were field-tested;
names of clients who have had such systems in the water
for a reasonable length of time; and what the seller will do
in the event that the system clogs. Purchasers should be
aware that product testing should be performed during the
spring through the fall when veligers are in the water -not
in winter, when they pose little or no threat to intakes. Good
old North American know-how will most likely combine
with our 1990s market economy to produce some form of
high-tech offshore mechanical filtration devices over the
next several years. But until then, the best advice is "buyer
beware."
Sand
Filtration
for
Offshore
Controls
A different, proven approach for filtration of water at the
source end of a pipe is the use of buried intakes and sand
filters. These types of filters are used in Europe and parts
of the Great Lakes for small municipal and industrial water
supplies with flow requirements of up to approximately
20
million gpd (75.71 million Ipd), but can be downsized to
handle the flow requirements
of groupings
of private
residences or even single residences.
Infiltration
Galleries
One form of buried intake is the infiltration
gallery. This
consists of porous intake pipes or well screens laid in
trenches excavated
in the bed of a lake or river. The
trenches are backfilled with sand and gravel and covered
over with larger crushed stone or cobble. A pump draws
water downward
through the sand and gravel which
obstructs the passage of zebra mussel veligers and other
organic and inorganic particulate material such as detritus
and silt (Fig. 8). The anoxic (oxygen-starved)
conditions
that exist within such filter beds create a very hostile
environment,
killing veligers trapped therein. Such filters
generally have flow rates of 0.5 to 1.0 gpm (1.89 to 3.79
Ipm) per square foot (.09 square meter) of filter surface.
General dimensions
for an infiltration gallery suitable to
reliably serve a residence requiring 250 to 400 gpd (946.35
to 1514.16 Ipd) are a 4-inch ( 10.16 centimeter) diameter
-6"
"'
Cobble/Gravel
~
f r3'
~t
t
1
To
~
pump
,"
-/""
Lake or
Stream Bed
t
J
~
Gravel
Filter
cloth
The time period between
backwashes will depend upon
the amount of water drawn
through the filter on a daily basis and the amount of particulate matter in the water. If the
homeowner's pump is not sufficiently powerful to accomplish
this, it may be necessary for a
plumbing contractor to perform
the operation utilizing a more
powerful portable pump. If a
gallery cannot be backwashed,
it may be necessary for the filter
sand to be manually "fluffed up"
or replenished by a diver.
Raised
4" Perforated pipe
Figure8.ln an infiltration gallery, a pump draws river/lake water downward into porous intake
pipes or well screens laid in sand- and gravel-filled trenches excavated in the bed of the river/
lake. Zebra mussels and other particles are removed
from the water as it passes through the
..or
sand
and
gravel.
The
trenches
are
covered
with
crushed
stone
or cobble
to protect
against.
Fill Sand
Filters
A form of sand filtration, the
raised fill sand filter, eliminates the trenches and replaces
them with a shallow layer of
gravel placed directly on a lake
b e d u pon w h 'Ich perfo .
river
,
wave and ice scouring. Such filters generally have flow rates of 0.5 to 1.0 gallons per minute
(gpm) per square foot of filter surface,
perforated pipe or well screen placed into a trench 4.0 feet
long, 4.0 feet deep, and 2.0 feet wide (1.22 meter by 1.22
meter by .61 meter), filled with a one foot layer of washed
gravel, covered by a sheet offiltercloth, and backfilled with
at least three feet of coarse sand which contains no fine
particles (e.g., silt), and protected by a cover layer of
cobbles. Readers may notice
that this alternative resembles
,,;,""CCc"C~cr,-,
ra.ted plpe.s or well screen ~re
laid. The pipes are covered with
a raised fill of gravel and sand
that is then covered with gravel
and crushed stone or cobble (Fig. 9). This raised fill sand
filter functions in the same way that an infiltration gallery
functions, with water drawn down through the sand and
gravel into the pipes, excluding mussel veligers and other
particulate materials. General dimensions for this type of
a septic system leach field operating in reverse, drawing water in ratherthan discharging it.
As water is drawn through
the sand portion of infiltration
galleries, mussel larvae and
juveniles, as well as silt and
other particulate matter will fill
in the spaces between the
grainsofsand.lnaddition,sand
will tend to pack and cake as
water is drawn through it, leading to the formation of cracks
through which larger particles
may pass into the water intake
system. For these reasons,
infiltration galleries must be
designed in such a manner as
to allow for backwashing of the
filter sand. This is usually accomplished by periodic reversa! of the water flow, pumping
filtered water from the shore
back through the filter gallery .
To PU~~--:::\
?
---
/--6"
Gravel
-2-3':
/
-12.
~
/
Filter cloth
I
Gravel
8' Gravel
""'
Lake
Figure
9. In a raised fill sand filter, perforated
placed
on the river/lake
is then covered
pipesorwell
bed. The pipes are covered
with gravel
and crushed
stone
screen
with a raised
or Stream
Bed
are laid upon a layer of gravel
fill of gravel
and sand which
or cobble.
7
~
sand filter, suitable to provide 250-400 gpd (946.35 to
1514.16 Ipd) to a private residence are: 4.0 feet (1.22
meters) of 4-inch (10.16 centimeters) diameter perforated
pipe or well screen, placed on a bed of 8.0 inches (20.32
centimeters) of gravel, buried 1.0 foot (.31 meter) deep
under gravel, covered with filter cloth and a layer of 2 to 3
feet (.61 to .91 meter) of sand, and protected with a 6 inch
(15.24cm) layerofgravel and crushed stone. This system
greatly resembles a raised fill septic leach field in
reverse.
As with infiltration galleries, raised fill sand filters should
be designed to be periodically backwashed.
Both the infiltration gallery and the raised fill sand filter
are subject to scouring (erosion) by storm waves and ice.
They are also subject to eventual clogging by fine silt and
clay from adjacent soils, and organic particulate materials
in the water drawn through the filter, not related to the
zebra mussel problem. The pipes should be entirely
embedded in gravel or wrapped with filter fabric to prevent
sand from migrating into the pipe perforations. It is recommended that at least three or four such pipes be placed to
ensure an adequate water supply for extreme events, or
that the filters be designed to allow for periodic backflushing
to remove the buildup of silt and clay particles.
Enclosed
or Prefabricated
Sand
material. Since zebra mussels do not normally attach to
sand, colonization of the open top surface should be
minimal. Unless the filter is placed in water deep enough
to be below storm wave scour, some rip rap (large rocks)
should be placed around it to prevent undermining or
shifting. Enclosed or prefabricated sand filters should be
less expensive to construct than infiltration galleries or
raised fill beds. Their smaller capacity makes them more
suitable for seasonal cottages than for year-round residences.
As with infiltration galleries and raised fill sand filters,
prefabricated sand filters should be designed to be periodically backwashed.
A number of commercial prefabricated sand filters are
now on the market. No independent review of these filters
is available, however, the concept they utilize (drawing
water through sand into a porous pipe) is sound, suggesting such filters may have a good likelihood of success.
Once again, readers should investigate any such product
to determine where and when it has been used and what
the rate of success has been. It is important that the filters
have been tested or installed (and in operation for a
season) in waters infested by zebra mussels and not
merely tested against silt and algae.
In-the-Iake sand filtration should prove successful for
removal of zebra mussels and other larger planktonic
animals and plants, but by itself is not intended to
provide potable water. Additional treatment at the house
end of the pipe, by chlorination, may still be needed to
Filters
While the expense of one of these sand filters may be
justified for a year-round residence, this might not be true
for a seasonal cottage with a lower water demand. A
possible
alternative
type of
sand filter for such situations is
the enclosed or prefabricated
sand filter. In this approach, a
Concrete vault open at top and
filled with sand above filter cloth
concrete, steel, or plastic box,
with a perforated pipe running
lengthwise through it, is filled
with coarse sand, placed into
the waterbody, and hooked up
to the residence's intake pipe
(Fig. 10). General dimensions
are: 4 to 6 feet (1.22 to 1.83
meters) of perforated pipe or
well screen with 6 inches ( 15.24
centimeters) of gravel beneath,
above, and on both sides of
the pipe and 24 to 36 inches
(61 to 91 centimeters) of sand
above the pipe. A sheet of filter
cloth should be used between
the sand and gravel. Existing
concrete
castings,
such as
septic tanks or burial vaults,
could be utilized as the containment structure. The top is
not placed onto the container,
allowing water to be drawn
downward through the sand
into the pipe excluding mussel
veligers and other particulate
8
r
To pump
"'
/
I
f
Lake or
Stream Bed
/
~,
~
\
1 0'/
/8-
Filter cloth
on top of gravel
~,
<,
"-t.
4" Perforated pipe imbedded in gravel
Figure 10. An enclosed or prefabricated sand filter constructed of a perforated pipe running
lengthwise through a concrete, steel, or plastic box filled with coarse sand and placed into a
waterbody is a lower cost alternative suitable for seasonal or weekend cottages.
disinfect for bacterial contamination. Readers should
consult their county Cooperative Extension Service or
health department for more information on potable
water supplies.
Possible environmental impacts of these in-the-Iake
sand filter alternatives include: the temporary degradation
of localized water quality due to an increase in turbidity
during excavation and backfilling; the disturbance of naturallake or river bottom habitats during construction; and,
a change in bottom habitat type from natural to humaninfluenced substrate. Turbidity impacts can be mitigated
through the use of trenching equipment (such as that used
by utility pipeline contractors) rather than backhoes to dig
the trenches and through the use of silt screens around the
excavation site. With the infiltration gallery and the raised
sand filter, habitat impacts may be in part offset by the
provision of new bottom habitat in the form of the stone
cover material. The enclosed or prefabricated sand filter
may help to minimize habitat impacts by having a smaller
"footprint" or area of disturbance than the other filter beds.
All of these in-the-Iake sand filter alternatives will almost
certainly require permits from state natural resource management
agencies
(DECs,
DNRs,
etc.).
A
nonenvironmental drawback of these alternatives is the
rather high initial cost of construction.
Ceramic and Cartridge
Filters
Several ceramic and cartridge filters intended for use on
the intake (lake) end of the pipe are now on the market.
Readers interested in these products should ascertain
how long they have been in service in mussel-infested
waters, what the porosity is (it should be a small enough
opening that no life stages will be passed live into the
intake pipe), how often they need to be backwashed
(some need to be manually backwashed, some are automatic), and how often they need to be replaced with new
material.
Removing
from
Zebra
the Offshore
Mussels
Component
Another approach to controlling zebra mussels in the
offshore component is to allow a certain amount of clogging in the intake pipe followed by periodic mechanical
cleaning of the system (remember, the onshore component is always protected by its own filtration/chlorination
system). Such cleaning may be mechanical orthermal. To
facilitate mechanical cleaning of an intake pipe, itwould be
advisable to install a cieanout "V" at the shore end of the
pipe to provide access to the intake. It should be noted that
many people have replaced older metal pipes with new,
more easily worked with PVC pipe. In terms of zebra
mussel control, this may pose a major problem: researchers have found that zebra mussel larvae tend to have a
preference for settling on PVC materials. PVC is even
used for settlement plates in many experiments and
monitoring systems. For the long term, readers might
consider the use of copper or galvanized pipes.
Snaking
For pipes that are short enough and that have easy
access from the shore end, cleaning can be as simple
and low-tech as running a modified plumber's snake
through the pipe on a periodic basis. This may not be
possible for very long pipes. Once the pipe is snaked,
the debris must be removed by pumping the pipe at a
high rate, and the debris-Iaden water must not be
allowed to enter the household distribution system. The
effectiveness of this method depends upon the design
of the pipeline and the intensity of the infestation.
Snaking is not effective in pipes with sharp, short radius
bends or anywhere the infestation is so great that the
amount of dislodged mussels might prevent their effective removal from the pipe or obstruct the progress of
the snake through the pipe.
Suffocation
and Desiccation
Since zebra mussels "breathe" oxygen as they draw
water over their gills, oxygen deprivation (suffocation),
accomplished by sealing off pipes long enough for the
water to lose all of its dissolved oxygen, can be used as
a control method. Mussels' demand for oxygen is greatest in warm water; therefore, oxygen deprivation tends
to work best in summer. Two or three days exposure to
water with no dissolved oxygen at 73.5°F to 75°F
(23.06°C to 23.89°C) should result in 100 percent zebra
mussel mortality. Unfortunately, this means that any
pipe treated in this manner must be able to be shut down
and sealed for a number of days. To use this control
strategy in year-round residential water systems, a
second intake pipe should be added, allowing one pipe
to be closed down for cleaning while water is pumped
through the second.
A similar use of dual piping, most useful for seasonal
cottages not using their intakes during the wintertime, is
the installation of short dual pipes laid above the bed of
the lake or river. When one pipe becomes clogged, it
can be pulled from the waterbody, allowed to dry out
completely, killing the mussels in it, and cleaned while
pumping continues through the second pipe. To utilize
this method in a year-round home, the main pipe, buried
for protection against freezing, would be used only after
the water temperature has dropped below the temperature needed for mussel spawning (approximately 50°F
[10°C]). Two short pipes, which could be alternately
pumped and cleaned, would be added to the system for
use during the summer spawning season.
Some people have advocated the movement of
intakes to deeper water in the hopes that this would
prove too cold for zebra mussel colonization and lack
sufficient supplies of mussel food to sustain large numbers of mussels. There is little data, however, to support
this idea. Zebra mussels easily survive near-freezing
water temperatures through Great Lakes winters with
little damage to established colonies below the ice
zone. Zebra mussels have been found colonizing down
to about 200 feet (60.96 meters) and veligers have been
9
found as deep as 220 feet (67.06 meters) in Lake
Ontario. For residential systems, deeper intakes would
seem, therefore, to hold little potential for success.
For a weekend cottage using only small amounts of
water for nonpotable uses, the use of a very short plastic
pipe that could be disconnected and laid on the shore at
the end of a weekend and reattached when the cottage
is next inhabited might be a very practical control
strategy. A "last resort" mechanical control for any
extreme situation is the removal and replacement of
clogged piping.
Thermal Treatment
Another effective and environmentally sound method of
controlling zebra mussels in intake pipes is systematic,
periodic flushing of intakes with heated water. Local
resource management agencies should, however, be
consulted to determine whether the amount of hot water
that might get into the environment would require any
type of discharge permit.
Water temperatures must exceed 98.6°F (37°C) for
about one hour to ensure 100 percent mortality for
mussels acclimated to so°F (10°C) water. Water temperatures greaterthan 131°F (55°C) will result in almost
immediate death of most mussels of most sizes. After
the thermal flush, mussels will remain attached to the
inside of the pipe for several days; they must then be
removed by pumping the pipe at a high rate of flow.
Heat treatments may be performed by flushing a pipe
with hot water. The intake pipe cannot have a foot valve
that would restrict the flow of water from the shore or
would need a mechanically openable foot valve to be
treatable in this manner. A large hot water heater would
be needed to provide sufficient hot water for a heat
treatment because heat loss through pipe walls into
cold lake or river water is considerable. The discharge
of large amounts of heated water into a waterbody could
have negative local environmental impacts and may
require a discharge permit from state resource management agencies.
A more suitable alternative would involve the use of
a long steam hose connected to a portable steam
generator set up at the shore end of the pipe. This steam
hose would be tipped with a multidirectional nozzle and
would be fed into the pipe through the cleanout recommended on page 9, treating the inside of the intake pipe
with live steam. The more often the pipe is heat treated,
the more the number and size of mussels to be removed
from the pipe will be reduced. A number of plumbing
contractors are utilizing this technique to clean intake
pipes up to 200 feet long in the Finger Lakes. One
caution: steam lines cannot be sent through pipes that
10
have tight bends.
Chemical
Treatment
of the Offshore
Component
At this time, there are no reliable chemical treatment systems suitable for use in the offshore component of residential
water intakes. There is great
concern about potential negative effects of chlorine or
other chemicals on fish or other aquatic organisms in
lakes and rivers should any of those chemicals be
released into the environment. Homeowners should
not pour or backflush any chemicals down their water
intake pipes. Such chemicals could be illegal if discharged into surface waters, might be environmentally
harmful, might be harmful to human health, and might
not even be effective in controlling zebra mussels.
Before using any chemical treatment method, readers
are strongly advised to check with local environmental
regulatory agencies.
Long-
Term
Control
Socioeconomic
Alternatives
Most, if not all, of the alternatives described in this fact
sheet could be scaled up to meet the needs of more than
one residence. Multiresidence zebra mussel control
systems would have the benefit of reducing an
individual's installation costs and might also have the
environmental benefit of eliminating a proliferation of
smaller, less efficient (possibly poorly installed) systems. Taken to a large enough number, multiresidence
systems might facilitate the establishment of special
taxation districts to pay for the installation and operation
of a community-wide water treatment and zebra mussel
control system.
A long-term social solution to the problem of zebra
mussel fouling of residential water systems might be the
extension of public water to those areas not already
serviced by public water. This alternative would not be
inexpensive and would take some time to implement.
Acknowledgements
The author wishes to thank Dr. Andrew
Miller, U.S.
Army Corps of Engineers Waterways
Experiment
Station and Mr. Timothy Sinnott, New York State Department of Environmental
Conservation,
for their agencies' reviews of this fact sheet. Graphics were prepared
by Mr. Norman
Frisch,
Department
of Design and
Production,
State University
of New York College at
Brockport.
Single copies of this publication
llIinois-lndiana Sea Grant Program
University of Illinois
65 Mumford Hall
1301 W. Gregory Drive
Urbana, IL 61801-3608
(217) 333-9448
This publication resulted fom the
activities of the Great Lakes Sea Grant
Network, which consists of universitybased programs in 1IIinois-lndiana,
Michigan, Minnesota, New York, Ohio
and Wisconsin.
Michigan Sea Grant College Program
University of Michigan
2200 Bonisteel Boulevard
Ann Arbor, MI 48109-2099
(313) 764-1138
Minnesota Sea Grant College Program
University of Minnesota
1518 Cleveland Ave., No
Suite 302
Sto Paul, MN 55108-6001
(612) 625-1253
are available free of charge from:
New York Sea Grant
SUNY College at Oswego
Rich Hall
Oswego NY 13126-3599
(315) 341-3042
Zebra Mussel Information Clearinghouse
Morgan III
SUNY College at Brockport
Brockport NY 14420-2928
(716) 395-2516
(800) 285-2285
Ohio Sea Grant college Program
The Ohio State University
1314 Kinnear Road
Columbus OH 43212-1194
(614) 292-8949
Wisconsin Sea Grant
University of Wisconsin-Madison
1800 University Avenue
Madison, WI 53705-4094
(608)263-3259
...and
from Sea Grant Advisory
Services offices throughout
the
region. Contact your local Sea Grant program for bulk order prices.
11